Static Optimization and Forward Dynamics "Tutorial"

[Leif Eric Goebel]

Hello,

I am relatively new to OpenSim. I already worked through the three given tutorials provided by the official site. Now I am trying to work my way through the documentation (User's guide) and am stuck at Static Optimization and Forward Dynamics.

At Static Optimization/Getting Started with SO there is the figure with the inputs and outputs. The Problem is, that i do not have the subject01_Setup_StaticOptimization.xml file. And neither I have the subject01_simbody_adjusted.osim file.

In the user's guide from e.g. Inversee Kinematics or Inverse Dynamics I have the input file and everything works fine.

Now to my problem with Forward Dynamics. Again in the User's Guide there is the figure which shows the used input files. I have both the "gait2354_CMC_Actuators.xml" and "subject01_Setup_Forward.xml" files. However if I load them and press run i get results which are definately not natural. The legs of the model just twist and turn backwards while the toes do entire "flips".

(I already downloaded the models folder again just to be sure, that it is the newest version.)

Is there a way or a site with an (even more) detailed tutorial on forward dynamics? Or is there a place where I can download those files explicitly?

Best regards and thank you very much in advance.

[Dimitar Stanev]

Hi,

Now I am trying to work my way through the documentation (User's guide)

Bravo, the best place to start!

At Static Optimization/Getting Started with SO there is the figure with the inputs and outputs. The Problem is, that i do not have the subject01_Setup_StaticOptimization.xml file. And neither I have the subject01_simbody_adjusted.osim file.

You can look into the example files provided for gait2392 or gait2354, which ship with OpenSim, that contain setup files for all tools. The adjusted .osim model is the model acquired from the scaling tool. The .xml file of static optimization saves the tool setup.

https://github.com/opensim-org/opensim- ... 92_Simbody
https://github.com/opensim-org/opensim- ... 92_Simbody

Now to my problem with Forward Dynamics. Again in the User's Guide there is the figure which shows the used input files. I have both the "gait2354_CMC_Actuators.xml" and "subject01_Setup_Forward.xml" files. However if I load them and press run i get results which are definately not natural. The legs of the model just twist and turn backwards while the toes do entire "flips".

This is the normal behavior. If you actuate a model which is unstable by nature and perform a forward dynamics simulation small errors in the input will cause large deviations in the expected outputs. Forward dynamics methods are used typically in a closed loop scheme (e.g. CMC).

[Leif Eric Goebel]

Thank you very much. Everything is working now fine =)